1. Field of the Invention
The present invention relates to a device for magnifying displacement of a piezoelectric element and a method of producing the same. The present invention also relates to printing heads including such a displacement magnifying device.
2. Description of the Related Art
One common application for devices for magnifying the displacement of a piezoelectric element is in printing heads. Such devices have a piezoelectric element disposed between a frame base portion and a contact member, and magnify displacement of the contact member according to the expansion amount of the piezoelectric element. In this type of device, if a gap develops between the frame base portion or the contact member and the piezoelectric element, the displacement of the contact member is reduced due to the gap. This decreases the magnifying rate of the displacement to the expansion amount of the piezoelectric element, which decreases the displacement magnifying rate of the device.
The expansion of the piezoelectric element is very slight. For the purpose of correctly transmitting the slight expansion to the device via the contact member, it is necessary to assemble the piezoelectric element between the frame base portion and the contact member without a gap and to apply a predetermined load to the piezoelectric element.
Such a displacement magnifying device is disclosed in European Laid-Open Patent Publication No. EP 0295 102 A2 published on Dec. 14, 1988, which corresponds to U.S. Pat. No. 4,874,978.
In the device disclosed therein as shown in FIG. 12, a pair of upper and lower wedge members 53a, 53b are interposed between the lower end of a piezoelectric element 55 and the upper end surface of a base portion 51a of a frame 51. Both wedge members 53a, 53b are formed of a material having a linear expansion characteristic different from that of the piezoelectric element 55, so that the expansion and contraction of the piezoelectric element 55 due to temperature change may be compensated for by the deformation of the wedge members 53a, 53b. Thus, the height of the piezoelectric element 55 above the upper surface of the base portion 51a is maintained at a constant level.
The engagement of the tapered surfaces of the wedge members 53a, 53b also applies on appropriate compression load to the piezoelectric element 55, so that the piezoelectric element 55 is supported in a fixed manner between the frame 51 and a contact member 54 without a gap. Therefore, the displacement amount of the piezoelectric element 55 in accordance with the applied voltage is accurately transmitted to a magnifying mechanism 57 to actuate a printing wire 56.
However, the above device requires a pair of mating wedge members in the narrow space of the print head. This causes difficulties in the assembly process which results in increased production cost.